The following abbreviations are herewith defined, at least some of which are referred to within the following description of the prior art and the present invention.    1× EVDV 1× Evolution Data and Voice    1× RTT 1 times Radio Transmission Technology    AAA Authentication Authorization and Accounting    ACH Access Channel    APN Access Point Name    AN Access Network    AMBR Aggregate Maximum Bit Rate    AKA Authentication Key Agreement    BCM Bearer Control Mode    CC Control Channel    CDMA Code Division Multiple Access    DNS Domain Name System    DRC Data Rate Control    DOS Data over Signaling    eAN evolved Access Network    EAP Extensible Authentication Protocol    eHRPD evolved High Rate Packet Data    ePCF evolved Packet Control Function    E-TRAN Evolved Terrestrial Radio Access Network    E-UTRAN Evolved Universal Terrestrial Radio Access Network    HSGW Home Serving Gate Way    HSS Home Subscribber Server    IMSI International Mobile Subscriber Identity    IP Internet Protocol    IP-CAN IP Connectivity Access Network    LTE Long Term Evolution    NAI Network Access Identifier    NW Network    PBA Proxy Binding Acknowledgement    PBU Proxy Binding Update    PCRF Policy and Charging Rules Function    PCO Protocol Configuration Options    PDN Packet Data Network    P-GW PDN Gate Way    PPP Point to Point Protocol    QoS Quality of Service    RAN Radio Access Network    RFC Request For Comments    RTC Reverse Traffic Channel    SPR Subscription Profile Repository    TCH Traffic Channel    TS Technical Specifications    UE User Equipment    UMB Ultra Mobile Broadband    UMTS Universal Mobile Telecommunications System    VSNCP Vendor Specific Network Control Protocol
LTE is a new radio access technology that will need to inter-work with the existing CDMA technology. FIG. 1 (PRIOR ART) is a block diagram illustrating an architecture of an E-UTRAN/EPC access network based on the new LTE radio access technology and an architecture of an eHRPD access network based on the existing CDMA radio access technology. Those skilled in the art are familiar with the architectures and functionalities of the E-UTRAN/EPC access network and the eHRPD access network. Thus, for clarity only the UE, eAN/PCF, HSGW, AN-AAA, PCRF, HSS, PDN-GW and SPR which happen to be relevant to the present discussion are described in detail herein while other well known components like the eNodeB, MME, Serving Gateway, HRPD BTS etc. are not described in detail within this document.
There are two handoff methods which currently exist today that can be used when a UE moves from the E-UTRAN/EPC access network (for example) based on the new LTE radio access technology to the eHRPD access network (for example) based on the existing CDMA radio access technology. The two handoff methods are known as the optimized handoff and the non-optimized handoff. The optimized handoff uses the S101 interface between the E-UTRAN access network and the eHRPD access network to allow the UE to establish and maintain the eHRPD radio session and HSGW context. This minimizes the delay (mute time) before the UE can send and receive packets after moving to the eHRPD access network. The non-optimized handoff generally requires the UE to establish an eHRPD radio session and HSGW context after moving to the eHRPD access network. However, it is possible that the HSGW already has partial context for the UE, which somewhat reduces the delay (mute time) before the UE can send and receive packets. These two types of non-optimized LTE-eHRPD handoffs are described in greater below in with respect to FIGS. 2-3 (PRIOR ART).
Referring to FIGS. 2A-2B (PRIOR ART), there is a signal flow diagram illustrating a non-optimized LTE-eHRPD active mode handover for the case when the eAN/ePCF and the HSGW have not saved any eHRPD context. The following messages or message sequences are exchanged in order to perform this type of non-optimized LTE-eHRPD active mode handover:                1. The UE is in an active mode while attached to E-UTRAN. Based on some trigger, the UE decides to perform cell reselection to eHRPD AN. The cell re-selection decision can be made at any time when the UE is attached in the E-UTRAN. The eNodeB may be involved in redirecting the UE to eHRPD.        2. The UE follows eHRPD procedures to establish a session with the eAN.        3. The UE, eAN and AN-AAA perform device level authentication procedures.        4. The UE acquires the necessary eHRPD resources to setup a traffic channel with the eAN.        5. The eAN/ePCF and HSGW exchange A11 messages to setup the default A10 (SO 59). The A11-RRQ contains the “tunneled mode indicator” set to ‘0’ to indicate to the HSGW that the UE is operating on the eHRPD radio. If the “tunnel mode indicator” is not present, then the HSGW always assumes that the UE is operating on the eHRPD radio.        6. The UE and HSGW perform LCP negotiation and select EAP-AKA' as the authentication protocol.        7. The authentication procedures are initiated and performed involving the UE, the HSGW, the 3GPP2 AAA and the 3GPP AAA Server (not shown here). In the roaming case, there may be several AAA proxies involved. The PDN-GW address is determined at this point: The AAA/HSS sends subscription data to the HSGW. The subscription data contains the list of all APNs that the UE is permitted to access and an indication about which of those APNs is the Default APN. The subscription data also contains the NAI will be used to identify the UE in Proxy Binding Update and Gateway Control Session Establishment messages. This information is cached at the HSGW on behalf of the attaching UE. If the subscriber profile did not include an absolute PDN-GW address then a DNS look up may be performed to determine the PDN-GW address. At the end of this step, the Authentication phase is complete. Also, the HSGW has received the subscription profile of the UE from the HSS/AAA.        8. The UE sends a VSNCP Configure-Request to the HSGW. The UE makes the assumption that the HSGW has maintained partial context from the previous time that the UE had established context on eHRPD.        9. The HSGW may perform Gateway Control Session Establishment procedure with the PCRF. If performed, the HSGW indicates the possible bearer control modes according to the UE capability provided in step 7 and its own capability. The PCRF selects the bearer control mode to be used. The PCRF may also query the SPR to retrieve the subscriber profile.        10. The HSGW sends a Proxy Binding Update to the PDN-GW in order to establish the new registration as per 3GPP: TS 29.275 V.8.5.0 “Proxy Mobile IPv6 (PMIPv6) based Mobility and Tunneling Protocol; Stage 3; (Release 8)” December 2009 (the contents of which are incorporated herein by reference). The HSGW uses the NAI received in step 6 to identify the UE. If the VSNCP message in step 7 does not identify a requested APN, the HSGW will use the default APN acquired from HSS/AAA during Authentication and Authorization procedures to choose the PDN-GW. If the VSNCP message in step 7 identifies a requested APN that is authorized to the user, the HSGW will use that APN to choose the PDN-GW.        11. The PDN-GW performs a PCRF interaction to establish the IP-CAN session as per 3GPP: TS 23.203 V.8.8.0: “Policy and charging control architecture, (Release 8)” December 2009 (the contents of which are incorporated herein by reference).        12. The PDN-GW responds with a Proxy Binding Acknowledgement. PBA to the HSGW as discussed in 3GPP: TS 29.275.        13. The HSGW sends a VSNCP Configure-Ack (PDN-ID, APN, PDN Address, PCO, Attach Type, and Address Allocation Cause) message to the UE over the main service connection. The PDN Address Information may contain an IPv4 address for IPv4 and/or an IPv6 Interface Identifier for IPv6. Additional configuration options (e.g., IPv4 Default Router Address) are included if they are present in the Configure-Request. The Protocol Configuration Options parameter may be included to indicate the Selected Bearer Control Mode, if the Protocol Configuration Options parameter was included by the UE in the corresponding VSCNP Configure-Request and indicated support for NW Requested Bearer Control.        14. The HSGW sends a VSNCP Configure-Request message to complete the protocol specified in IETF RFC 3772: “PPP Vendor Protocol” May 2004 (the contents of which are incorporated herein by reference). The message includes the PDN-ID configuration option. This message also contains the APN-AMBR if received from the HSS/AAA.        15. The UE responds with a VSNCP Configure-Ack message. The UE includes APN-AMBR, if it received APN-AMBR in step 13 and if the UE supports APN-AMBR.        16. The UE, RAN (not shown), HSGW and PCRF proceed to re-establish dedicated bearers based on the Bearer Control Mode.        17. Dedicated bearer can now flow over the eHRPD network with the proper QoS.            Note: This type of non-optimized LTE-eHRPD active mode handover has a mute time of around 3075 ms for the UE initiated BCM and 3015 ms for the network initiated BCM.
Referring to FIGS. 3A-3B (PRIOR ART), there is a signal flow diagram illustrating a non-optimized LTE-eHRPD active mode handover for the case when the eAN/ePCF and the HSGW have saved at least partial eHRPD context. The highlighted areas 300a and 300b which include the following steps: (1) eHRPD session establishment; (2) device authentication (query IMSI); and (3) EAP over PPP based authentication have been eliminated from the handoff process due to a partial context of the UE being saved by the eAN/ePCF and the HSGW (compare to FIGS. 2A-2B). The following messages or message sequences are exchanged in order to perform this type of non-optimized LTE-eHRPD active mode handover:                1. The UE is in active mode and currently attached to E-UTRAN. Based on some trigger, the UE decides to perform cell reselection to eHRPD AN. The cell re-selection decision can be made at any time when the UE is attached in the E-UTRAN. The eNodeB may be involved in redirecting the UE to eHRPD.        2. The UE acquires the necessary eHRPD resources to setup a traffic channel with the eAN.        3. The ePCF recognizes that the A10 session associated with the UE is available, and initiates an ‘Active Start’ to the HSGW.        4. The HSGW may retrieve the UE context from the HSS/AAA, including the IP address(es) of PDN-GW(s) currently in use by the UE.        5. The UE sends a VSNCP Configure-Request to the HSGW. The UE makes the assumption that the HSGW has maintained partial context from the previous time that the UE had established context on eHRPD.        6. The HSGW may perform Gateway Control Session Establishment procedure with the PCRF. If performed, the HSGW indicates the possible bearer control modes according to the UE capability provided in step 5 and its own capability. The PCRF selects the bearer control mode to be used. The PCRF may also query the SPR to retrieve the subscriber profile.        7. The HSGW sends a Proxy Binding Update to the PDN-GW to establish the new registration as per 3GPP: TS 29.275 V. 8.5.0: “Proxy Mobile IPv6 (PMIPv6) based Mobility and Tunneling Protocol; Stage 3; (Release 8)” December 2009 (the contents of which are incorporated herein by reference) The HSGW uses the NAI received in step 5 to identify the UE: If the VSNCP message in step 5 does not identify a requested APN, the HSGW will use the default APN acquired from HSS/AAA during Authentication and Authorization procedures to choose the PDN-GW. If the VSNCP message in step 5 identifies a requested APN that is authorized to the user, the HSGW will use that APN to choose the PDN-GW.        8. The PDN-GW performs a PCRF interaction to modify the IP-CAN session as per 3GPP: TS 23.203 V.8.8.0: “Policy and charging control architecture, (Release 8)” December 2009 (the contents of which are incorporated herein by reference).        9. The PDN-GW responds with a Proxy Binding Acknowledgement PBA to the HSGW as discussed in 3GPP: TS 29.275.        10. The HSGW sends a VSNCP Configure-Ack (PDN-ID, APN, PDN Address, PCO, Attach Type, and Address Allocation Cause) message to the UE over the main service connection. The PDN Address Information may contain an IPv4 address for IPv4 and/or an IPv6 Interface Identifier for IPv6. Additional configuration options (e.g., IPv4 Default Router Address) are included if they present in the Configure-Request. The Protocol Configuration Options parameter may be included to indicate the Selected Bearer Control Mode, if the Protocol Configuration Options parameter was included by the UE in the corresponding VSCNP Configure-Request and indicated support for NW Requested Bearer Control.        11. The HSGW sends a VSNCP Configure-Request message to complete the protocol specified in IETF RFC 3772: “PPP Vendor Protocol” May 2004 (the contents of which are incorporated herein by reference). The message includes the PDN-1D configuration option. This message also contains the APN-AMBR if received from the HSS/AAA.        12. The UE responds with a VSNCP Configure-Ack message. The UE includes APN-AMBR, if it received APN-AMBR in step 10 and if the UE supports APN-AMBR.        13. The UE, RAN (not shown), HSGW and PCRF proceed to re-establish dedicated bearers based on the Bearer Control Mode.        14. Dedicated bearer can now flow over the eHRPD network with the proper QoS.        
Note: This type of non-optimized LTE-eHRPD active mode handover has a mute time of around 688 ms for the UE initiated BCM and 628 ms for the network initiated BCM.
Unfortunately, if the UE participates in either of these two types of non-optimized handoffs the user will experience a mute time of at least about 628 ms which is not suitable for voice and many data services. Accordingly, there has been a need and still is a need to address this shortcoming and other shortcomings associated with these two types of non-optimized handoffs. This need and other needs have been addressed by the present invention.